Ruomei Gao
Email: [EMAIL PROTECTED]
On Sat, 6 Apr 2002 [EMAIL PROTECTED] wrote:
> >
> > > 1, Some of the exchange points are layer 2 facilities, then why do they need
> > > register IP addresses? Furthermore, those IP addresses do appears in the
> > > traceroute traces (from the skitter data of caida). Does this mean that these
> > > IP addresses are actually in use?
> >
> > Nearly all exchange points are layer 2. This means that they consist of a
> > layer 2 switch, normally Ethernet, on rare occasions ATM or frame relay,
> > or even something more exotic. The participating ISPs bring routers,
> > which they all connect to the switch. Each of those routers must have an
> > IP address in order to communicate with the others, and the IP addresses
> > must all be within the same subnet. That being the case, the correct
> > procedure is for a block of addresses to be allocated to the exchange,
> > rather than through any one of the ISPs, so that the rest of the
> > participants aren't dependent upon any one ISP which might be providing
> > the address space. Also, that way no ISP is forced to provide transit for
> > the exchange-point addresses, which theoretically don't need it.
>
> Er, -ALL- exchanges have a layer2 component. Some institute
> policy at layer 3. Since, in general, we are talking about
> INTERNET exchanges it makes sense that IP comes into play.
> If there is a shared medium that is used as a single broadcast
> domain, then a common subnet makes life easier for everyone.
> It is possible to use divergent networks (see Sleepy Bills (woodcock)
> list) on the same shared media. His list argues that these
> distinct subnets are unique exchanges. My take is that they
> are not but that is a nit argument. There are lots of ways to
> slice the exchange point.
>
> > So yes, those addresses are very much in use, but in somewhat the same way
> > that the /30 on a point-to-point link would be. As a means for the two
> > adjacent routers to communicate, and pass on traffic which is coming from
> > and going to points much more distant.
>
> What he said. It is the Internet after all.
>
> > > 2, How do you categorize the exchange points into large/local IXs,
> > > transit/peering IXs (besides look into the peering policies)? From the number
> > > of participants? Or from who are the participants?
> >
> > The difference between a local and a regional exchange is typically one of
> > size of participants. It isn't a technical difference, so it might be a
> > little hard to arrive at complete consensus on, with respect to any
> > particular exchanges. It's probably safe to say that in the U.S., PAIX in
> > Palo Alto, MAE-East ATM, and Equinix Ashburn are regional exchanges, that
> > in Europe the LINX and AMS-IX are regional exchanges, and that in Asia
> > JPIX, NXP-ISP2, and HKIX are regional exchanges. They're where large
> > regional ISPs would go to peer with ISPs from outside the region. A
> > regional exchange would often be thought of as one that an ISP from
> > outside the region would go to first.
>
> only the very brave or very foolish will attempt such
> catagorization. Posh Bill (norton) clearly points out that
> the value of an exchange, like beauty, lies in the eyes/network
> of the beholder. local/regional - peering/transit.... the
> key thing is "whats in it for me?"
>
>
> > The difference between a peering exchange and a transit exchange is a much
> > more easily technically-defined difference: a peering exchange is one
> > across which, by and large, the participants just exchange peering routes.
> > A transit exchange is one across which many of the participants are
> > exchange full transit. The consequences of this distinction are pretty
> > far-reaching, and generally mean that only one large peering exchange can
> > exist in a region, and it'll be inexpensive, whereas several smaller, more
> > expensive transit exchanges can coexist in the same region. Phil Smith,
> > Keith Mitchell, and I will be presenting a paper on the topic at the next
> > NANOG in Toronto.
>
> Humph. Difference w/o (significant) distinction.
> If -ANY- isp provides transit off the exchange fabric,
> does that make it a transit exchange? If not, why not?
>
> And what about exchanges that have -NO- routing protocol
> at all? (can you say ARP.... sure you can.) Not peering
> or transit. Or are they?
>
> For me, the key point is that an exchange acts as an aggregation
> point for the participants. Generating value off aggregation
> can take many forms. Peering and Transit are but two vectors
> that are effected by aggregation.
>
>
> --grumpy bill (manning)
>
